The present invention relates to a variable magnification copying apparatus and, more particularly, to an optical system for such an apparatus which includes a fixed focal length lens for forming an image of the document to be copied, moving mirror pairs to adjust object and image conjugates for any selected magnification and means for moving the lens from one segment of the optical path to another upon selection of a predetermined magnification value.
A variety of copiers are commercially used which produce reduced or enlarged copies of original documents. A preferred optical system incorporates optical elements which scan a document line by line. The following patents illustrate the various optical systems used to enable the variable magnification.
U.S. Pat. Nos. 4,498,759 and 4,538,904 are illustrative of optical systems which scan a stationary document placed in an object plane. Full rate/half rate mirrors move to adjust object and image conjugates, while a fixed focal length lens moves along the optical path to selected positions, depending upon magnification selection.
U.S. Pat. No. 5,063,406 illustrates an optical system where the document is moved past a fixed exposure station and where a zoom lens is adapted to enlarge and reduce the scanned image.
U.S. Pat. Nos. 4,040,733; 4,172,658 and 4,639,121 disclose variable magnification systems where the imaging lens moves along the optical path to different magnification locations and also moves perpendicular to the axis to maintain registration. A compact optical design is a desirable objective when designing a variable magnification copier. Prior art efforts to provide a compact design are disclosed in U.S. Pat. Nos. 4,027,963 and 4,374,619. These patents incorporate a half lens element which includes a mirror in the lens assembly, reducing the need for an additional folding mirror elsewhere along the optical path, thus making the system more compact. Reduction copying in a limited space is also disclosed in "Optical Reduction System", Xerox Disclosure Journal, Vol. 5, No. 1, January/February 1980, page 97.
The present invention is directed towards a novel, variable magnification optical system which incorporates mirror pairs movable along an optical path to adjust object and image conjugates during magnification changes, but which does not require lens translation along the optical path. Rather, the lens, which in a preferred embodiment, is a constant focal length wide angle lens, is maintained in a fixed position so long as magnification selections are made within a first range. The lens is in fixed position along one segment of a folded optical path. Upon selection of a magnification lying within a second magnification range, the lens, in a preferred embodiment, is moved perpendicular to the optical path to an adjacent parallel segment of the optical path, placing the lens either closer to the photoreceptor (for reduction) or further from the photoreceptor (for enlargement). While it is known to move a lens perpendicular to the optical path, from U.S. Pat. No. 4,040,733, referenced supra, these references do not disclose moving the lens so as to intersect the optical path at a different location. Japanese publication 60-78439 (Hashimoto) discloses a lens which both moves along the optical path and, at some point, is moved diagonally to a non-parallel optical path segment.
More particularly, the present invention is directed to a variable magnification copying apparatus for producing reduced or enlarged copies of an original document moving through a document exposure zone at a variable rate of movement in response to magnification values selected by an operator, said apparatus including:
means for producing output illumination to illuminate incremental line portions of the document as it passes through said exposure zone, line images reflected from said document being transmitted along an optical path, folded into a plurality of segments, onto a photoconductive surface,
a symmetrical lens for forming an optical image of said original document on said photoconductive surface, said lens movable from a fixed position on a first segment of the optical path to a fixed position on a second segment of the optical path,
a first mirror assembly positioned along the optical path between the lens and the exposure zone, said mirror assembly movable along the optical path,
a second mirror assembly positioned between the lens and the photoconductive surface, said second mirror assembly movable along the optical path,
means for moving said lens and first and second mirror assemblies in response to signals representing a selected magnification value, said movement resulting in adjustment of the object and image conjugates for the magnification values selected, and
control means for receiving signals representing said magnification values and for operating said means for moving the lens and mirror assemblies to the required positions along the optical path, said control means further adapted to change the rate of movement of the original document through the exposure zone in response to said magnification value signals.